Using stripped-down versions of living cells, researchers have confirmed which proteins allow certain bacteria to breathe iron and other metals when oxygen isn't available. Shewanella oneidensis is often found in oxygenated environments but can also thrive without the gas if it must, thanks to energy-generating chemical reactions that transfer electrons from inside its cells to outside minerals that contain metals such as iron. Previous studies identified a particular set of three cell-membrane proteins involved in this electron transfer process, but subsequent research suggested that the protein found on the external side of the cell membrane, dubbed MtrC, transferred electrons too slowly to explain the microorganism's rate of metabolism. In a new series of lab tests, researchers created tiny, cell-sized capsules that lacked a living cell's metabolic machinery but included all three cell-membrane proteins in a simplified outer layer. Measurements showed that rates of electron transfer from substances inside the capsules were more than 1 million times faster than those seen previously in MtrC-only experiments and were more than sufficient to fuel Shewanella in oxygen-poor environments. Besides shedding light on the iron-breathing bacterium's metabolic tricks, the new findings may help researchers harness Shewanella to make biobatteries known as microbial fuel cells.
Sid Perkins, Science Magazine